1. Field of the Invention
This invention relates to self-aligned dynamic threshold field effect devices and the method of making such devices. More specifically, this invention relates to insulated gate field effect devices formed as isolated semiconductor devices, such as with silicon-on-insulator (SOI) technology, where the gate is connected to the body of the device to provide dynamic threshold operation.
2. Description of Related Art
The demand for high performance and low power consumption microelectronic devices has increased with the expansion of the market for portable electronic devices such as laptops, cell phones and the like. Dynamic threshold devices, including insulated gate field effect transistors (IGFETs), MOSFETs and similar devices offer this desirable combination by their ability to operate at extremely low voltages, such as at 0.6 volts or less.
Dynamic threshold devices generally operate by connecting the body of the device to the gate of the device. Making this connection causes the threshold voltage, i.e., the voltage at which the device begins to conduct, to be reduced as compared to conventional CMOS technology which typically has a threshold voltage of 0.6 volts or more.
The reduction in threshold voltage (which is actually a dynamically changing threshold voltage) allows an ultra-low power supply voltage to be used. The reduction in the power supply voltage substantially reduces power consumption of the device. This generally reduces battery weight, decreases the heat dissipation requirements and provides other advantages for the designer of portable electronic devices.
Because the body of each dynamic threshold device must be electrically isolated from the body of each adjacent device, dynamic threshold devices typically are constructed with SOI or bulk triple well technologies.
One difficulty with the production of devices of this type has been the space required for the body contact. Prior designs have placed the body contact along the entire length of the device. This uses valuable device space, but is necessary due to the relatively low conductivity of the body. Another problem has been the necessity for separately aligning the body contact relative to the device.
The present invention addresses these problems by introducing a buried self-aligned highly doped low-resistance body, located below the gate dielectric. The low resistance of the body allows a relatively small area at an end of the device to be used to make connection to the body region. The low-resistance body is constructed in a way which accurately aligns it and places it precisely next to, but not abutting, the source and drain regions.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of making a dynamic threshold field effect device where the surface area used for the body connection is reduced as compared to previous designs.
It is another object of the present invention to provide a method of making a dynamic threshold field effect device having a buried low-resistance body region.
A further object of the invention is to provide a method of making a dynamic threshold field effect device having a buried low-resistance body region wherein the body region is formed by a self-aligning process relative to the gate dielectric and the gate.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.